1. Field of the Invention
This invention relates to apparatus and method for aligning misaligned adjacent vertebrae and more particularly to a new and improved partible vertebrae alignment screw with axially shiftable thread sections that will threadedly couple to a tapped thread cut into the misaligned vertebrae, relatively slide to relatively shift the vertebrae, and threadedly decouple from the aligned vertebrae while maintaining the integrity of the tapped thread.
2. Description of the Prior Art and Objects
Spinal injuries, diseases and other degenerative disorders of the spine have caused substantial problems and pain to a substantial number of patients. Various devices have been provided heretofore for preventing progressive degeneration and instability of the spine. One such technique has involved bone fusions which fuse adjacent spinal vertebrae to each other to prevent relative movement therebetween. Such fusions frequently follow the removal of all or a portion of a disc normally found between the adjacent vertebrae.
To aid in the fusion process, hollow threaded cages, packed with bone chips or other bone growth inducing substances, have been disposed in the intervertebral space between the adjacent vertebrae and threadedly coupled to confronting portions of the adjacent vertebrae. Such fusion cages are illustrated in U.S. Pat. No. 4,961,740 issued to Charles D. Ray, et al, on Oct. 9, 1990; U.S. Pat. No. 5,015,247 issued to Gary K. Michaelson on May 14, 1991; U.S. Pat. No. 5,906,616 issued to Paul W. Pavlov, et al on May 25, 1999; and U.S. Pat. No. 5,947,971 issued to Steven D. Kuslich on Sep. 7, 1999.
Prior to threadedly coupling the fusion cage to the vertebrae, confronting portions of adjacent misaligned vertebrae are drilled and tapped to provide a thread for receiving the thread of the fusion cage as more particularly illustrated in the PLIF Surgical Technique Manual 2.0, Ray Threaded Fusion Cage(trademark), published by Surgical Dynamics Inc, 111 Glover Avenue, Norwalk, Conn., which is incorporated hereby by reference as though fully set forth herein. The vertebrae to be fused together should be properly aligned prior to the fusion. When the adjacent vertebrae are out of alignment with each other, which is a condition sometimes referred to as spondylolisthesis, they are to be moved back into alignment prior to the insertion of the fusion cage. Toward this end, apparatus, such as that disclosed in the German Patent Publication No. 197 50 382.9 dated Nov. 13, 1997, has been utilized to realign the vertebrae.
The German Patent Publication No. 19750382.9 discloses a screw which can be threaded into a thread previously tapped into confronting portions of misaligned vertebrae. Portions of the screw in the aforementioned German patent publication are anchored to adjacent vertebrae and axially shifted relative to each other to shift the vertebrae into alignment. The screw is then unturned and a hollow threaded cage is turned into the threaded space vacated by the screw. With the aforementioned prior art German construction, it is difficult to insure that the partial screw threads on each of the partible halves are in helical alignment with the partial screw threads on the other partible half so that the helical thread tapped into the adjacent vertebrae is not damaged by the partial screw threads on the partible halves being out of helical alignment with each other and not following the same helical path. Accordingly, it is an object of the present invention is to provide a new and novel method and apparatus for repositioning misaligned vertebrae.
It is another object of the present invention to provide new and novel vertebrae aligning apparatus which is threadedly received by a tapped thread provided on confronting portions of adjacent misaligned vertebrae and which can be removed, without damaging the tapped thread after portions of the screw have been shifted to align the vertebrae.
Apparatus for shifting vertebrae for the reduction of spondylolisthesis is illustrated in U.S. Pat. No. 5,601,556 issued to Madhavan Pisharodi on Feb. 1, 1997, including an insert that is disposed between adjacent vertebrae and then rotated 90xc2x0 before and after shifting of the vertebrae. The Pisharodi device is not threaded into and out of the vertebrae and is not concerned with preserving the integrity of a tapped screw thread which threadedly receives a fusion cage.
Another object of the present invention is to provide a new and novel vertebrae alignment tool which will align misaligned vertebrae including axially partible screw thread sections having complementally formed partial screw threads thereon that can be moved to any selected one of a plurality of axially spaced apart positions in which the partial screw threads on one screw thread section are helically aligned with the partial screw threads on the other screw thread section.
Still another object of the present invention is to provide a vertebrae alignment tool of the type described which includes a new and novel locking device for locking the partible screw thread sections together when they are being threaded into and out of the adjacent vertebrae.
Yet another object of the present invention is to provide apparatus for aligning misaligned vertebrae of the type described including an alignment nut which is threadedly received by axially partible screw sections in any selected one of a plurality of axially spaced apart positions to insure that the partial screw threads on one-half of the screw are held in helical alignment with the partial screw threads on the other half of the screw as the screw is being threadedly coupled to misaligned vertebrae and threadedly decoupled from aligned vertebrae.
Still yet another object of the present invention is to provide a new and novel vertebrae repositioning tool of the type described which includes an alignment nut that is threadedly received on axially partible screw halves having first and second pluralities of partial screw threads that are helically aligned to form a helical thread on a screw that is threadedly coupled to adjacent misaligned vertebrae and a locking nut for locking the alignment nut to the screw halves to prevent relative movement therebetween as the screw is being threadedly coupled to misaligned vertebrae and decoupled from aligned vertebrae.
A further object of the present invention is to provide alignment apparatus for aligning misaligned vertebrae including new and novel elongate bodies for mounting partible screw halves which are axially slidably coupled to each other.
A still further object of the present invention is to provide alignment apparatus of the type described including new and novel mechanism for axially shifting the elongate bodies relative to each other to axially shift the screw head.
Another object of the present invention is to provide a new and novel method of aligning first and second vertebrae including axially locking a pair of screw halves together as the screw halves are being threadedly coupled to and decoupled from adjacent vertebrae and for unlocking the screw halves and axially shifting the screw halves between the coupling and decoupling steps.
It is another object of the present invention to provide apparatus for shifting and aligning adjacent vertebrae in preparation for, and during the process of, securing the vertebrae with a fusion cage screw sometimes sold under the trademark xe2x80x9cRay Threaded Fusion Cage(trademark)xe2x80x9d.
Another object of the present invention is to provide new and improved vertebrae alignment method and apparatus which will prepare more qualified candidates for the cage screw method of fusing vertebrae than that which existed in the prior art.
A still further object of the present invention is to provide a method of aligning misaligned adjacent vertebrae including the steps of: threadedly coupling an axially partible vertebrae displacing head, having first and second abutting screw halves, provided with half screws, which are helically aligned to form a helical screw thread, coupled to adjacent misaligned vertebrae; axially relatively shifting the screw halves opposite directions to shift the misaligned vertebrae into alignment, detachably locking the screw halves together in the axially displaced positions with the half threads in helical alignment to preclude axial movement therebetween, and axially unthreading the vertebrae displacing head from the vertebrae with the abutting screw halves held together to prevent relative axial shifting therebetween.
Other objects and advantages of the present invention will become apparent to those of ordinary skill in the art as the description thereof proceeds.
Apparatus for repositioning misaligned vertebrae comprising an alignment head, having first and second axially partible screw halves forming first and second screw thread sections which cooperate in a plurality of axially spaced positions to form a helical screw on the head, which is rotatable about a longitudinal axis in a first direction between the vertebrae to a position in which the first and second screw thread sections each threadedly engage only one of the vertebrae and oppositely rotatable to an unthreaded position removed from the vertebrae after the vertebrae are repositioned; mechanism for relatively axially shifting the first and second axially partible screw halves, while threadedly coupled to separate ones of the adjacent vertebrae, in opposite directions to relatively properly reposition the vertebrae relative to each other, and mechanism for axially detachably holding the first and second screw halves together, with at least a portion of the first screw thread section in helical alignment with a portion of the second screw thread section, to preclude relative axial shifting of the first and second screw thread sections when the head is rotated in the opposite direction and threadedly decoupled from the aligned vertebrae. A method of aligning vertebrae without damaging a tapped threaded provided in adjacent misaligned teeth is also contemplated.